The most challenging tools for musicians and sound engineers are nonlinear processors such as dynamics processors, valve simulators and exciters. The successful application of these audio processors depends on the appropriate control of these devices. A variety of interactive control parameters influences the resulting sound quality.
The primary purpose of this chapter is to enable the reader to attain a fundamental understanding of different types of nonlinear processors and the special properties of nonlinear operations applied to the audio signal. Dynamics processors need a careful consideration of the interaction of thresholds and time constants to achieve sonic purity and avoid harmonic distortion. On the other hand, nonlinear processors are used for the simulation of valve amplifiers or nonlinear audio systems, where a special kind of nonlinearity provides a sound distortion with an accepted sound characteristic. We have presented the basics of nonlinear modeling and focused on the combination of filters and nonlinearities. Several applications demonstrate the importance of nonlinear processors. The basic building blocks of the previous chapters such as filters, delays and modulators/demodulators are particularly useful for exploring new, improved nonlinear processors.